Measurement of Aerodynamic Breakup of Non-Newtonian Drops by Digital In-Line Holography

Aerodynamic fragmentation of bulk liquid into small droplets is an essential spray process that occurs in a variety of combustion systems. The aerodynamic breakup of non-Newtonian fluids, such as aerospace propellants, bio-fuels, fire-fighting liquids, thermal barrier coatings, water-gel explosives, paints, etc, is involved in many important applications. Non-Newtonian fluids differ from Newtonian fluids in that they do not exhibit a linear shear stress-strain rate relationship. They are employed when the liquid is desirable to have a low viscosity during spray formation (high strain rate) and a higher viscosity when on a target (low strain rate). This useful rheological behavior leads to a significantly different breakup mechanism of non-Newtonian fluids compared to that of Newtonian liquids. Unfortunately, there are limited experimental studies on the aerodynamic breakup of non-Newtonian drops. This is probably due to the difficulty in measuring fragments of complex morphologies. Digital in-line holography (DIH) provides simultaneous measurements of the particle size and position with unique access to three-dimensional (3D) information. Previous applications have demonstrated its applicability to arbitrary-shape particles, capability of extracting 3D morphologies, and effectiveness in characterizing the aerodynamic breakup of Newtonian drops. In the present study, the aerodynamic breakup of non-Newtonian drops is characterized using DIH. The measured characteristics including breakup morphologies, fragment/droplet size distribution and velocity distributions, demonstrate the effectiveness of DIH as a diagnostic tool for non-Newtonian fluids.